Therapeutic embolization or occlusion of blood vessels may be used to treat a variety of vascular and non-vascular conditions including cerebral and peripheral aneurysms, arteriovenous malformation, uterine fibroids and various tumors. One commonly used agent for embolizing blood vessels is the embolic coil, a permanently implanted coiled wire structure which, when implanted into a blood vessel, occludes the vessel by causing thrombosis where it is deployed. Embolic coils may have different lengths and/or cross-sectional diameters, in order to fit into and occlude vascular structures of varying sizes. In use, the coils are delivered through a microcatheter in a narrow-diameter elongated configuration (e.g. to fit within a 3 Fr catheter lumen). Once deployed into the vessel, the coil may assume a complex 3-D shape such as a helix, a spiral, a J-shape, or a birds-nest shape, and may include thrombogenic fibers or bundles of fibers along its length. Embolic coils are highly flexible, and can be delivered through narrow or tortuous vascular structures, but when occlusion of relatively large vascular structures is desired, multiple coils may be necessary to achieve full occlusion.
These coils have typically been placed at the desired site using a catheter and a pusher. The site is first accessed by the catheter. In treating peripheral or neural conditions requiring occlusion, the sites are accessed with flexible, small diameter catheters, which may be guided to the site through the use of guidewires and/or flow-directed means such as balloons at the distal end of the catheter. Once the site has been accessed, the catheter lumen is cleared (i.e., the guidewire is removed if a guidewire has been used), and the coil is placed in the proximal end of the catheter and advanced through the catheter with a pusher. When the coil reaches the distal end of the catheter it is advanced into the vessel and deployed. This technique of plunging the coil from the distal end of the catheter has undesirable limitations. First, because of the plunging action of the pusher during deployment, the positioning of the coil at the site cannot be controlled to a fine degree of accuracy. Second, once plunged from the catheter, it is difficult to reposition or retrieve the coil if desired. Indeed, another device, called a retriever, must be threaded through the catheter to snare the coil to reposition or retrieve it.
The coil is typically connected to the pusher or another structure within the catheter and must be detached. This detachment is typically facilitated by the use of an electrolytically severable link or a mechanical coupling. While current detachment mechanisms are generally reliable, they may not release the coil when triggered 100% of the time. In the case of mechanical detachment mechanisms in particular, improving detachment reliability may involve undesirable trade-offs such as increasing the size and/or cost of parts used in detachment mechanisms.